title: Melanocortin 4 receptor becomes an ACTH receptor by coexpression of melanocortin receptor accessory protein 2.
abstract: Melanocortin 2 receptor (MC2R) is the only canonical ACTH receptor. Its functional expression requires the presence of an accessory protein, known as melanocortin receptor 2 accessory protein 1 (MRAP1). The vertebrate genome exhibits a paralogue gene called MRAP2, which is duplicated in zebrafish (MRAP2a and MRAP2b), although its function remains unknown. In this paper, we demonstrate that MRAP2a enables MC4R, a canonical MSH receptor, to be activated by ACTH with a similar sensitivity to that exhibited by MC2R. Both proteins physically interact and are coexpressed in the neurons of the preoptic area, a key region in the control of the energy balance and hypophyseal secretion in fish. ACTH injections inhibit food intake in wild-type zebrafish but not in fish lacking functional MC4R. Both MRAP1 and MRAP2a are hormonally regulated, suggesting that these proteins are substrates for feed-back regulatory pathways of melanocortin signaling. Fasting has no effect on the central expression of MRAP2a but stimulates MRAP2b expression. This protein interacts and is colocalized with MC4R in the tuberal hypothalamic neurons but has no effect on the pharmacologic profile of MC4R. However, MRPA2b is able to decrease basal reporter activity in cell lines expressing MC4R. It is plausible that MRAP2b decreases the constitutive activity of the MC4R during fasting periods, driving the animal toward a positive energy balance. Our data indicate that MRAP2s control the activity of MC4R, opening up new pathways for the regulation of melanocortin signaling and, by extension, for the regulation of the energy balance and obesity.
authors.affiliation: Department of Fish Physiology and Biotechnology, Instituto de Acuicultura de Torre de la Sal, 12595 Torre de la Sal, Ribera de Cabanes, Castellón, Spain. jm.cerda.reverter@csic.es.
authors.forename: Maria
authors.initials: M
authors.lastname: Josep Agulleiro
authors.forename: Raúl
authors.initials: R
authors.lastname: Cortés
authors.forename: Begoña
authors.initials: B
authors.lastname: Fernández-Durán
authors.forename: Sandra
authors.initials: S
authors.lastname: Navarro
authors.forename: Raúl
authors.initials: R
authors.lastname: Guillot
authors.forename: Eirini
authors.initials: E
authors.lastname: Meimaridou
authors.forename: Adrian J L
authors.initials: AJ
authors.lastname: Clark
authors.forename: José Miguel
authors.initials: JM
authors.lastname: Cerdá-Reverter
mesh_terms: D000324:Adrenocorticotropic Hormone / Q000502:physiology; D000818:Animals; D001629:Bezafibrate / Q000494:pharmacology; D002352:Carrier Proteins / Q000235:genetics / Q000378:metabolism*; D002149:Energy Intake; D005260:Female; D015870:Gene Expression; D057809:HEK293 Cells; D006801:Humans; D006854:Hydrocortisone / Q000502:physiology; D047908:Intracellular Signaling Peptides and Proteins; D008297:Male; D047492:Peroxisome Proliferator-Activated Receptors / Q000819:agonists / Q000378:metabolism; D025941:Protein Interaction Mapping; D021381:Protein Transport; D044105:Receptor, Melanocortin, Type 4 / Q000235:genetics / Q000378:metabolism*; D018043:Receptors, Corticotropin / Q000235:genetics / Q000378:metabolism*; D014284:Triiodothyronine / Q000502:physiology; D015027:Zebrafish; D029961:Zebrafish Proteins / Q000235:genetics / Q000378:metabolism*
chemical_list: D002352:Carrier Proteins; D047908:Intracellular Signaling Peptides and Proteins; C000588930:MRAP2b protein, zebrafish; D047492:Peroxisome Proliferator-Activated Receptors; D044105:Receptor, Melanocortin, Type 4; D018043:Receptors, Corticotropin; D029961:Zebrafish Proteins; C461479:mc4r protein, zebrafish; D014284:Triiodothyronine; D000324:Adrenocorticotropic Hormone; D006854:Hydrocortisone; D001629:Bezafibrate